Interactions between eruptive activity and sector collapse at Anak Krakatau, Indonesia

Lead Research Organisation: University of Birmingham
Department Name: Sch of Geography, Earth & Env Sciences

Abstract

Anak Krakatau volcano, Indonesia, collapsed catastrophically on 22nd December 2018, forming a landslide-generated tsunami that caused over 400 deaths on surrounding coastlines. Very few volcanic landslides of this size and type, known as sector collapses, have been studied in detail. Because of this, our understanding of the factors that lead to sector collapse, and therefore our capacity to forecast such events and their associated hazards, remains relatively limited. Although there have been few historical examples of large volcanic landslides, they are common on longer, geological timescales and occur across all volcanic settings. The collapse of Anak Krakatau thus provides an important opportunity to improve our knowledge of this fundamental volcanic process.

Anak Krakatau is the volcanic island that formed after the devastating eruption of Krakatau (also known as Krakatoa) in 1883, first emerging above sea level in 1929. Approximately half of the subaerial island of Anak Krakatau was removed by its recent sector collapse. The collapse occurred during an ongoing, relatively low-intensity eruption, similar to the type of activity that had characterised previous decades. However, satellite observations suggest that this style of activity changed around the time of the collapse, to a much more powerful explosive eruption. The precise timing of this change, and its potential role in the collapse, is something we will explore in detail in this research. Following the collapse, explosive activity continued and may have changed yet again, as seawater interacted with shallow erupting magma. This later stage of activity erupted large volumes of new material, rapidly filling the landslide scar and extending the island coastline in the days after the collapse.

Our research will determine the specific role of eruptive activity in the sector collapse of Anak Krakatau. We will address whether changes in eruption behaviour, involving the ascent of fresh magma, preceded the collapse and thus acted as a trigger; or whether it was the collapse itself which led to the powerful explosive eruption, by suddenly depressurising the shallow magma stored beneath the volcano. We will also define the nature of eruptive activity that took place immediately after the collapse. In this phase of the eruption, material appears to have been ejected at a very high rate, and we will test the hypothesis that the collapse destabilised the underlying magma system, leading to a change in eruption behaviour. Such processes may be common at volcanoes affected by large sector collapses, forming part of a cycle of destruction and regrowth, but are currently poorly understood.

Our work will draw upon detailed field sampling of eruption deposits spanning the collapse period. Field datasets will be interpreted alongside satellite imagery and other remote observations, numerical models that simulate eruption processes, and analyses of the chemical and textural record of magmatic processes preserved in our eruption-deposit samples. Together, our results will allow us to identify changes in the storage conditions, ascent rate and eruptive behaviour of magmas involved in different stages of activity. Our results will allow us to explore controls on the timing of the sector collapse, the role of eruptive activity in the collapse, and the impact the collapse itself had on the underlying magma system. By producing a comprehensive record of the Anak Krakatau collapse and eruptions, we will advance our understanding of volcanic sector collapses in general. We will also develop a much clearer picture of eruption processes and instabilities at Anak Krakatau, which will inform hazard mitigation plans for potential future landslides as the volcano regrows.

Planned Impact

This research will provide a comprehensive understanding of the volcanic processes involved in the sector collapse of Anak Krakatau, including the role of eruptive activity in the build up to collapse, the nature of explosive activity that accompanied the collapse, the impact of collapse on the underlying magma system, and the nature of the volcanism that led to rapid post-collapse regrowth of the island. As well as providing significant insights into eruption-associated sector collapses in general, these results have a broad importance to non-academic stakeholders including Indonesian hazard monitoring agencies and those working in the field of tsunami modelling and tsunami hazard mitigation.

Hazard monitoring agencies: Results, including technical summaries, will be shared fully with the appropriate Indonesian agencies responsible for volcanic and tsunami hazards: the Centre for Volcanology and Geological Hazard Mitigation (CVGHM), and the BMKG (the Meteorology, Climatology and Geophysical Agency, responsible for tsunami warning). We have already been in contact with relevant stakeholders to discuss our research plans, and these relationships will be developed further through pre-fieldwork meetings with these agencies. The unforeseen nature of the Anak Krakatau collapse highlights the unpredictability of sector collapses and the challenges involved in mitigating their effects. The controls on sector collapse remain poorly understood, but our detailed analysis of the event will identify the role of eruptive activity in the collapse, and will also provide a clearer understanding of post-collapse regrowth at Anak Krakatau, enabling future activity and growth to be monitored in the context of recent events. Our evaluation of a variety of remote sensing data will also help directly inform future developments of hazard monitoring at Krakatau. Collectively, our results will provide a much improved basis for forecasting future instabilities, and for developing landslide-tsunami monitoring efforts and mitigation plans on that basis.

Tsunami modellers: More generally, our results will form important additions to a comprehensive landslide-source and tsunami dataset for the Anak Krakatau event, making it the best constrained example of a large scale volcanic-island tsunami. This example can be used as a benchmark dataset against which tsunami models can be tested and improved, and then used for future landslide-tsunami hazard modelling scenarios. This is important to tsunami modellers in both academic and non-academic contexts, including those involved in coastal flood risk management and tsunami preparation in all volcanic settings, and the reinsurance sector. Results will be shared with international tsunami modelling groups (via active collaborations with S. Grilli, U. Rhode Island) and by providing a volcanological summary of the event to relevant stakeholders (e.g. to the quarterly technical meeting of the Intergovernmental Oceanographic Commission).

Wider public engagement: Our work is also likely to be of wide public interest, particularly given the effects of the Anak Krakatau collapse and its international media coverage, as well as broader awareness of Krakatau as a source of hazardous volcanic eruptions. One benefit of this type of research is increased awareness, education and engagement with scientific topics. We will distribute results through public talks, community events, museum exhibits and will also aim to publicise our research through local and national media.

Publications

10 25 50
 
Description Interpretation of data and results from this research is ongoing and this seciton will be updated in due course. The overall aim of the research was to evaluate whether a shift in magmatic activity drove the collapse of Anak Krakatau, or if the reverse was true - that the collapse initiated the observed changes in eruptive activity. This question is important in helping address whether monitoring data could identify precursory signals of volcanic lateral collapses. The project retrieved a full set of samples spanning the collapse and has enabled a detailed reconstruction of eruptive activity. These are being evaluated in terms of both physical and chemical shifts in eruptive processes, and their timing interpreted alongside monitoring data, satellite datasets and other observations.
Exploitation Route The outcomes will be relevant to volcano and tsunami hazard agencies globally in terms of improving the understanding of the triggers of volcanic lateral collapses, and giving insights into what signals may precede such an event. From this and other research, improved monitoring strategies can ultimately be developed. The results will also feed into improvements in landslide tsunami modelling - the outputs of this reserach are currently being used to develop updated constraints on the event parameters (landslide source) that will be tested against current numerical tsunami models. Results will be shared fully via Indonesian partners in the project to feed into regional hazard management strategies.
Sectors Communities and Social Services/Policy,Environment,Leisure Activities, including Sports, Recreation and Tourism,Government, Democracy and Justice,Other

 
Description The results of this project have been communicated widely to a public audience, as noted in more detail above. In Indonesia, a series of talks given in Bandung were livestreamed to a public audience and led to a number of questions in a public discussion. The aim of the talks was to explain the aims and initial results of our reserach, but also to discuss the nature of lateral collapse hazards on volcanic islands, following the recent devastating impact of the Anak Krakatau collapse and tsunami. We have also reached public audiences directly in the UK through a series of outreach events (museum exhibitions, public and school group talks and informal discussions), and via media coverage of this project and broader NERC-funded reserach investigating Krakatau (e.g. media coverage on multiple news websites following the AGU conference). Results are being fully shared with Indonesian collaborators and we are continuing to work together on this research. Through this route, our findings will be disseminated to hazard management agencies in Indonesia, adding to the understanding of this event and the potential for lateral-collapse tsunami hazards at Anak Krakatau and other Indonesian volcanoes, and thereby informing future monitoring strategies.
First Year Of Impact 2019
Sector Communities and Social Services/Policy,Education,Leisure Activities, including Sports, Recreation and Tourism,Government, Democracy and Justice
Impact Types Societal

 
Description Volcanic eruption processes at Krakatau volcano, Indonesia 
Organisation Bandung Institute of Technology
Country Indonesia 
Sector Academic/University 
PI Contribution Through this project we have strengthened research collaborations with the Bandung Institute of Technology (Mirzam Abdurrachman), which has built on previous partnerships developed by a co-investigator on the project (M Cassidy). The team from Bandung offered substantial field support in Indonesia during this project, and research support (leading the drone based element of the research project), and we are continuing to work together on outputs from this project. The collaboration has also led to an upcoming research visit and is likely to support future research in the region between the two teams. We have shared data and samples resulting from the field survey, presented a series of talks in Bandung, and will continue to analyse and publish results together.
Collaborator Contribution As noted above, the partners contributed significantly to field support and led the drone-based part of the field survey; they have also contributed subsequent data and samples to the project, and the Indonesian and UK teams are continuing to work together on the project.
Impact The collaboration is not multi-disciplinary. Co-authored research publications are in preparation and will be reported here in due course.
Start Year 2019
 
Description Media coverage of project related research at AGU conference 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Outputs from this research project, alongside other NERC funded reserach projects investigating Krakatau (Tappin et al., eruption generated tsunamis; and Hunt et al., marine survey of Anak Krakatau) was covered widely following presentations at the AGU conference. This included articles on several international websites and a discussion on a BBC radio programme.
Year(s) Of Engagement Activity 2019
 
Description Multiple public talks and exhibits related to the research project (West Midlands region) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Several talks and outreach events have been given by the investigators involved in this project. Examples include an exhibit at a recent arts and science evening event (Lapworth Lates) held in the Lapworth Museum, Birmingham, where an exhibit showed samples, video and images relating to the research, as a starting point to stimulate discussions with a broad public audience. Other examples include a presentation of the reserach at the upcoming Pint of Science festival (Birmingham), and a talk to school and local interest groups at the Shropshire Geological Society.
Year(s) Of Engagement Activity 2019,2020
 
Description Series of public reserach talks at Bandung Institute of Technology, Indonesia 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Following the field element of this project in Indonesia, and building on our partnership with Indonesian collaborators, four members of the reserach team presented a series of talks at Bandung Intsitute of Technology, Indonesia, about the aims of the project and initial results. The talks were given in the university but also live-streamed to a public audience. Following the talks, there was an open discussion between the speakers and the audience, including several questions from the public audience.
Year(s) Of Engagement Activity 2019
URL https://www.itb.ac.id/news/read/57208/home/peneliti-itb-bersama-para-geologist-inggris-lakukan-penel...